The invention relates to a process of making models, molds, near net shape parts, and other integral objects using an imagewise exposure of a dispersion of components to radiation. The process is based on homogenizing the components of the dispersion to form an alloy which have properties different from the properties of the dispersion or its individual components.
Layer-by-layer solid imaging techniques, including stereolithography and selective laser sintering, have been used to produce models, mold patterns, and near net shape production parts. Stereolithography provides high accuracy and excellent surface finish, but does not normally allow for productions of objects in engineering materials such as nylon or ABS. Selective laser sintering can produce objects in nylon or polycarbonate but cannot produce objects of full density, and generally produces objects having low surface quality.
U.S. Pat. No. 5,354,414 describes imagewise formation of an integral object which can be separated from the non-imaged regions. Processes of brazing, soldering and welding are disclosed for producing the integral object.
U.S. Pat. No. 4,575,330 describes generation of three-dimensional objects by creating a cross-sectional pattern of the object on the surface of a fluid medium. The physical state of the medium is altered to form successive cross-sectional layers and provide a step-wise laminar buildup of the desired object. As an example of a suitable change in physical state, the patent discloses free-radical curing of acrylate.
U.S. Pat. No. 5,474,719 describes a solid imaging process wherein high viscosity liquids are viscosity-reduced during coating and allowed to increase in viscosity during imaging steps. In particular, the compositions contain a photohardenable monomer and a photoinitiator, and the photohardening methods suggested involved free-radical polymerization, cationic polymerization, anionic polymerization, condensation polymerization, addition polymerization, and the like.
U.S. Pat. No. 4,938,816 describes a process for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The bulk density of the powder is increased prior to sintering or melting the powder by exposure. Attaining high bulk density of powders for sintering is difficult, however, and requires the use of substantial pressures.
It is known in the art that certain advantages are associated with providing at least one above solidus temperature component in a dispersion to be sintered. The advantages are, for example, improved wetting between the components, reduction of friction between the components to allow for greater densification, capillary forces which draw the components together and drive densification, and greater molecular diffusion between components during sintering. See, for example, R. M. German, Liquid Phase Sintering, Plenum Press, New York, 1985; and Eremenko et al, Liquid Phase Sintering, Plenum Publishing Corp., New York, 1970. These disclosures do not teach imagewise layer-by-layer formation of three-dimensional integral articles.
The invention comprises a process for producing three-dimensional integral objects by imagewise radiation of a dispersion of components A and B, comprising the steps of:
a) providing a dispersion of component A and component B;
b) forming the dispersion into a layer;
c) homogenizing the dispersion by the application of imagewise radiation to form an alloy of components A and B; and
d) repeating steps a)-c) by applying each successive layer of dispersion onto the previous layer, such that each new homogenized region becomes integral with the previous homogenized region to form a homogenized, integral, three-dimensional object.
Components A and B may be polymers, metals, ceramics, or combinations of these materials. The components A and B are capable of alloying, when exposed to imagewise radiation, to form an alloy of the two components A and B which is characterized by physical and/or chemical properties which are distinct from the physical and/or chemical properties of the dispersion of components A and B. The components are combined into intimate contact to form the dispersion, preferably with one component being in a liquid state or above solidus state, prior to homogenization. Following homogenization by imagewise exposure, the homogenized alloy article may be separated from the unexposed dispersion based on the difference in physical and/or chemical properties. For example, the homogenized alloy of components A and B may have a melting point different from the melting point of component A, the melting point of component B, or the melting point of an intimate dispersion of components A and B.